1. Field of the Invention
The present invention relates to a force feedback input device in which force feedback is provided to an operation member of the force feedback input device in accordance with the operating status and, in particular, to a stopper mechanism to restrict excessive displacement of the operation member.
2. Description of the Related Art
As input devices applied to, for example, a central “by-wire” control system of in-car electronic devices, a steer-by-wire steering system, a shift-by-wire gear change system, and a brake-by-wire braking system, force feedback input devices are known which includes an operation member that an operator manually operates, detection means, such as a position sensor, for detecting the operating status of the operation member, an actuator for providing force feedback to the operation member, and control means for controlling the actuator based on detection signals output from the detection means (refer to, for example, Japanese Unexamined Patent Application Publication No. 2002-149324, in particular, pages 3 to 5, and FIG. 3). Such force feedback input devices can provide various types of force feedback to the operation member in accordance with the direction and amount of movement of the operation member, and thereby can provide desired operation feeling to operations of the by-wire devices.
In these force feedback input devices, when the operation member is operated to an allowed maximum displacement, further displacement must be limited. To limit the displacement, a simple stopper mechanism is widely employed in which part of the operation member is brought into contact with a stopper fixed at a predetermined position.
Unfortunately, in the case where the allowed operations range, namely, the moving range of the operation member varies in accordance with use conditions, a stopper mechanism capable of changing the position of the stopper is essential to restrict excessive displacement of the operation member. In one known force feedback input device having this type of stopper, a rotary motor functions as an actuator that provides feedback force, such as sense of resistance, to the operation member, and the resistance force is increased by applying a large electric current to the motor when the operation member is displaced to an allowed limit of the operation range. However, since the known force feedback input device must apply a large electric current every time the operation member is displaced to an allowed limit of the operation range, power consumption is undesirably increased, which is a problem. In addition, the control method that increases the resistance force by applying a large electric current to the motor does not produce a distinct sense indicating that no more displacement of the operation member is possible, also referred to as “wall effect”. Consequently, this method does not provide satisfactory operability.
Some force feedback input devices are proposed to restrict undesirably increased power consumption by providing an electromagnetic brake, separately from the motor which provides force feedback to the operation member. According to this proposal, since the electromagnetic brake can easily produce a large braking force, the displacement of the operation member can be instantly stopped at a predetermined position. In practice, the reverse displacement of the operation member whose excessive displacement is limited must not be restricted. As a result, the braking force of the electromagnetic brake must not be too strong and, therefore, this force feedback input device cannot provide satisfactory operability.